Transcript Surveys Sampling

Do What Needs to Be Done Today.
The secret of happy successful living is to do
what needs to be done now , and not worry
about the past or the future.
Surveys Sampling
Simple
random sampling
Random digit table
Representative Sample

(Simple) random sample: Each group of units
of the required size from the population has
the same chance to be the selected sample.
Human Being Bias
Please pick one number between 0 and 9
randomly.
** count # of students picking numbers 4,5,6
and show them the human being bias.

Resources of Random Numbers
Random digit table
(p. 81 in Textbook)
 Random numbers generated by computer
software such as Minitab
(shown in lab)
** Minitab: Calc >> Make Patterned >> Simple
Set of Numbers; and then Calc >> Random
Data >> Sample from Columns

Example: Take 5 out of 300 randomly
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Number the units in the population starting at
1 using the same number of digits (eg. 001,
002, …, 300)
In a random digit table, choose any number
as the starting point, say row 2 column 3
(63753…)
From the starting point, read across the row
3-digit by 3-digit and get numbers from 001
to 300 to identify units
Example: 5 out of 300
From the table
63753 53067 79710 52555 72307 10223
27475 10484 24616 13466…
3-digit numbers: 637, 535, 306, 779, 710, 525,
557, 230, 710, 223, 274, 751, 048, 424, 616,
134…
Random Assignments
Goal: Wish to assign 9 subjects to 3 treatments
randomly.
Pick 1 out of 3 for each subject 
Treatment assignments: 3, 3, 3, 1, 2, 2, 3, 2, 2